The invention pertains to a window shade with a shade panel of the type indicated in the introductory clause of claim 1.
Many different designs of window shades with roll-up coverings for windows in buildings or for other openings are known, such as those designed as rolling shutters and rolling gates. In the basic vertical type of installation, the shade consists of a winding shaft at the top for winding up a shade panel onto the winding shaft and for unwinding it from the shaft to form a shade panel, the free-hanging end being weighted at the bottom by a rod.
In one particular design, the hanging shade consists of a thin, sheet-like panel, which has creases parallel to the winding shaft. EP 950 801 describes a window shade of this type. These creases give the surface of the panel a corrugated profile in the unwound state and give the wound-up panel roll a triangular profile.
This corrugated profile is perhaps advantageous as decoration for the surface of the panel, but it is also problematic, because it allows the shade to spring back and forth elastically in the longitudinal direction under tensile stress. As a result, the free-hanging shade panel weighted by the bottom rod can vibrate considerably during winding and unwinding. These vibrations impair the appearance of the shade and can also lead to malfunctions.
The invention is based on the task of improving a window shade of the type indicated in the introductory clause of claim 1 in such a way that the disadvantages cited above are avoided while at the same time the shade can be wound up and down smoothly.
This task is accomplished by the characterizing features of claim 1 in conjunction with the features of the introductory clause.
Additional solutions and embodiments of the invention form the objects of the subclaims.
The vibrations which occur during the winding and unwinding of shade panels, especially those with creases and the resulting corrugated profile, can be explained by the interaction of the following properties of the type of window shade considered here. The elastic surface of the shade panel works together with the bottom rod to create a spring-mass system, the resonance frequency of which varies with the length of the free-hanging part. If the shade roll has a certain profile such as a triangular profile, the tensile forces being transmitted to the panel increase and decrease periodically as the roll turns. These forces excite vibrations when they match the resonance frequency.
To solve this dynamic problem, therefore, control means are according to the invention installed upline of the winding shaft to vary the rotational speed of the winding shaft in such a way that the winding shaft has several periods in each revolution, the angular velocity changing in a predetermined manner in each period. This has the result of compensating for the out-of-round shape which may develop or which already exists on the winding shaft. In the case of a shade panel roll with an out-of-round profile, therefore, the tensile forces do not increase and decrease during the winding and unwinding operations. The shade panel moves up and down smoothly, without any vibrations.
The shade panel with creases can consist of plastic, metal, or some other elastic material.
A shade panel of plastic consists, for example, of polyester with a thickness of 0.01-0.15 mm. In one type of embodiment, the creases are parallel to the winding shaft, and the spacing between them is in the range of 7-40 mm, depending on the thickness of the panel, and the bending angle at the creases is 120-180 in the rotational direction of the panel roll.
A corresponding shade panel of metal consists, for example, of stainless spring steel with a thickness of 0.005-0.100 mm. The spacing of the creases is approximately 7-100 mm, depending on the thickness of the metal and on its modulus of elasticity.
The problem mentioned above occurs especially when the shade panel is provided with creases which allow the unwound surface of the shade panel to form a corrugated profile and the rolled-up panel to form a triangular profile on the winding shaft. The panel roll with a triangular profile has in this case approximately the shape of an equilateral triangle with rounded comers.
The effective roll radius which determines the linear movement of the shade panel varies accordingly between the maximum radius belonging to the comers and the minimum radius belonging to the sides. To compensate for this out-of-round profile, the control means vary the angular velocity in inverse proportion to the effective roll radius, so that the tangential velocity remains constant at the transition between the roll and the panel surface. The winding shaft thus has three periods, each with its own angular velocity curve. In correspondence with the geometry present here, the ratio between the minimum and maximum angular velocity is approximately 0.5-0.75.
The design of the control means can be basically either electronic or mechanical.
In the case of a purely mechanical design, the control means are installed between the winding shaft and the drive shaft. A reducing gear forms the control means in this case, in that it has at least one radial cam, which defines the periods with the changing angular velocity. In the case of a panel roll with a triangular profile, the cam is provided with three sections, so that the winding shaft acquires three periods, each with its own angular velocity curve.
The panel roll could also be rectangular or pentagonal, for example, in which case the reducing gear would be provided with cams capable of producing four or five periods.
The reducing gear can be designed in various ways. The following embodiments are explained below on the basis of a triangular panel roll.
In a first embodiment, the reducing gear is designed as a drive belt drive with drive belts passing around belt pulleys. The variation of the angular velocity is in this case achieved by giving the belt pulley connected to the winding shaft a triangular profile similar to that of the shade roll. The cam is thus on the belt pulley.
In a second embodiment, the control means can be designed as a synchronous belt drive with toothed belts passing over gearwheels, in which case the gearwheel connected to the winding shaft has a triangular profile. The cam is thus provided on the gearwheel. The second gearwheel, i.e., the one connected to the drive shaft, preferably also has a cam with a triangular, elliptical, or eccentric shape. It is obvious that the exact shape of these gearwheels with the cams will be designed in such a way that the toothed belt remains under uniform tension over the entire course of its revolution.
In addition, the reducing gear can be designed as a gearwheel transmission with eccentric, elliptical, or triangular gearwheels, in which case the gearwheel connected to the winding shaft is triangular. The cam is thus on the gearwheel. In the case of a combination of a triangular wheel with an elliptical wheel, the reduction ratio is 3:2, and in the case of a combination of a triangular wheel with an elliptical wheel, the ratio is 3:1.
In a special variant, several triangular gearwheels are arranged in a row. In this way, it is possible, if necessary, to span a large distance between the winding shaft and the drive shaft. The gearwheel connected to the drive shaft can also be elliptical or eccentric, so as to achieve, for example, a reduction of 3:2 or 3:1.
The transmission can also comprise one or more universal joints. In this case, advantage is taken of the principle that universal joints, the shafts of which are at an angle to each other, vary their angular velocity twice per revolution in accordance with a sine function. Because three periods per revolution are required to compensate for a triangular panel roll formed by a creased shade panel, a gear with a reduction ratio of 3:2 is installed between the universal joint and the winding shaft.
In the case of an electronic design, the drive shaft is connected directly to the winding shaft. Here the electronic speed control unit of the shade drive forms the control means which changes the angular velocity within each period.
When, for example, the shade panel has creases and the panel roll has a triangular form, the drive shaft will therefore change its angular velocity in each of three separate periods per revolution. Suitable electronic speed controllers, which can also include sensors for measuring rotational angles and rotational speeds, are already known to the expert.
In a variant of this embodiment, the basic rotational speed can be switched between two or more additional speed settings. The electronic speed control unit can be switched between at least two different velocity profiles per revolution. A signal transmitter is used to generate the switching signal for switching between one velocity profile and another when the shade panel has been unwound to a certain length. Changing the basic rotational speed in this way makes it possible to avoid resonance, the frequency of which varies with the length of the wound or unwound shade panel.